The SSSI comprises seven individual sites, spread over a 9-mile (14 km) radius around the towns of Camborne, Redruth and Helston, totalling an area of 53.9 hectares (133 acres).

The copper laden spoil tips, along with the derelict mine buildings, support populations of rare bryophytes (mosses and liverworts).

[3] On both of the Tolgus Tin Works sites grow the four main bryophyte species along with Pohlia andalusica, which produces capsules only at this location in Britain.

[3] The West Basset Stamps location supports the three main liverworts along with Pohlia andalusica, Cephaloziella stellulifera and the nationally scarce mosses Bryum pallescens and the capsule producing Gymnostomum viridulum, again only at this site in Britain.

[3] On the exposed areas of the spoil tips on Porkellis Moor can be found the three main liverworts as well as Pohlia andalusica.